시도 1. Stack 이용 → 통과

import java.util.*;

class Solution {
    public int[] solution(int[] progresses, int[] speeds) {
         Stack<Integer> stack = new Stack<>();
        int[] answer = {};
        for (int i = progresses.length - 1; i >= 0; i--) {
            stack.push(progresses[i]);
        }

        int day = 1;
        int idx = 0;
        int outCount = 0;
        while (true) {
            if (stack.isEmpty()) {
                answer = Arrays.copyOf(answer, answer.length + 1);
                answer[answer.length - 1] = outCount;
                break;
            }
            if ((stack.peek() + (day * speeds[idx])) >= 100) {
                outCount++;
                stack.pop();
                idx++;
            } else {
                if (outCount != 0) {
                    answer = Arrays.copyOf(answer, answer.length + 1);
                    answer[answer.length - 1] = outCount;
                }
                outCount = 0;
                day++;
            }
        }
        return answer;
    }
}

모범 답안

import java.util.ArrayList;
import java.util.Arrays;
class Solution {
    public int[] solution(int[] progresses, int[] speeds) {
        int[] dayOfend = new int[100];
        int day = -1;
        for(int i=0; i<progresses.length; i++) {
            while(progresses[i] + (day*speeds[i]) < 100) {
                day++;
            }
            dayOfend[day]++;
        }
        return Arrays.stream(dayOfend).filter(i -> i!=0).toArray();
    }
}